The popularity of very small satellites with masses around 10 kg or less, known as picosats, has grown in recent years with the introduction of the cubesat standardization. Individual cubesats have a size of 10 cm on each side (1U), and double (2U) and triple stack (3U) versions are also utilized. Due to their low cost and simplicity, previous cubesat missions have typically been university-based projects. However, there has been some significant interest recently from government agencies to further develop and enhance the cubesat buses (as well as slightly larger nanosat buses), and to assess the value of miniature payloads hosted by these very small satellite buses.
The majority of cubesats launched to date either tumble arbitrarily with no on-board attitude control, or utilize simple magnetic control to align the bus with the geomagnetic field lines. However, recently, there have been significant advancements in the development of miniaturized space weather and radio frequency payloads for cubesat applications, though most of these payloads require pointing knowledge and control of a few degrees or better. Cubesat-compatible attitude control units with miniature reaction wheels are available for such missions, but accurate and cost-efficient three-axis attitude knowledge is still very challenging for these small satellites. Some cubesat buses manage to avoid this problem by flying in an aerodynamically-favorable orientation, exploiting deployed arrays for passive aerodynamic control augmented with active momentum bias and magnetic damping control. Future cubesat buses can utilize miniature star trackers for very precise attitude knowledge (arc-seconds). However, star trackers tend to be very costly (>$100,000) and require greater size, weight, and power than less-accurate solutions. Furthermore, many cubesat missions simply do not need the high accuracy provided by expensive star trackers. Currently the most common three-axis attitude solution for picosat-class satellites is the combination of multiple sun sensors and a magnetometer, with the obvious loss of sun information whenever the satellite passes into eclipse, which can occur for as often as one-third of every orbit.
Accordingly, there remains a need for a small cost-effective attitude sensor for picosat-class missions that can provide continuous sub-degree three-axis attitude sensing in day or night operations.